I wouldn't say there are similarities to D&D (I have played only 3rd ed, though more RP than tactical). Blackguards is just like the usual turn based battlefield, so there are rolls, hexes etc... If you like to rage over rolls, this game is for you.

Now in terms of mechanics, the games are pretty much different, as Blackguards is based on a different P&P system. The main ones are:
1. There are no classes in this game - it offers you 3 archetypes (warrior, ranger, mage), but you can also build your own character from scratch. The only determinant at this point is whether your char will be able to wield magic or not (this cannot be changed later!).
2. You don't level up, instead you get Adventure Points that can later be spent on parameters (can be increased anytime, as opposed to D&D), skills, traits, special abilities, and spells (if one is a magic wielder).
3. Depending on the mixture of the above, your characters will have different walking range, different hit chance etc...
4. There are also some statuses in battles; besides some standard ones like poison, there are wounds. If someone gets wounded (there are up to three wounds), their chances of survival drastically fall - they lose their to-hit chance, walking range and are easier to hit. Usually wounds need a different treatment than usual HP.

Should you try it? In my opinion yes - the game can be quite challenging, though on normal difficulty you don't really have to use all the possible ways of winning (I haven't set a trap in the game). It offers some nice environmental actions, but the main challenge is pretty much the same throughout the game - don't get yourself killed, look out for traps and archers, overcome enemy who has more swords than you. Sometimes there are some obstacles like flame throwerers etc that you have to watch out for.
It can be a bit frustrating, but definitely is fun and I really sunk into it.

If you are still not sure, you can grab a playable demo from here.